Fluidization enhancers for oxidative dehydrogenation of hydrocarbons

Abstract

The present invention provides a method for the oxidative dehydrogenation of hydrocarbons to produce olefins and water, which method may include contacting the hydrocarbon with a particulate material that may include at least one oxygen transfer agent (OTA) and at least one fluidization enhancing additive in a fluidized bed. During at least a portion of the contact between the hydrocarbon and the particulate material, the fluidized bed may be at a temperature equal to or greater than the melting point of one or more materials of the oxygen transfer agent. In addition, during at least a portion of the contact between the hydrocarbon and the particulate material, the surface of at least a portion of the OTA may include a molten layer. The fluidization enhancing additive may not undergo reduction in the fluidized bed during the contact between the hydrocarbon and the particulate material and may be present in an amount that maintains sufficient fluidization of the particulate material.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of prior-filed provisional application No. 62 / 979,051, filed on February 20, 2020, the entire contents of which are hereby incorporated by reference herein.

[0003] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0004] This invention was made with government support under Grant No. DE-EE0008315 awarded by the U.S. Department of Energy. The U.S. Government has certain rights in this invention. Technical Field

[0005] Embodiments of the present disclosure relate generally to chemical processing, and more particularly to olefin production via oxidative dehydrogenation. Background Art

[0006] Light olefins, such as ethylene and propylene, are important building blocks for the manufacture of polymers such as polyethylene, polypropylene, polystyrene and many more polymers of commercial interest. More than 90% of global olefin production comes from high temperature steam cracking of naphtha or ethane and propane. The steam cracking process using a heating furnace is highly energy intensive and produces 1.5 to 2 tons of carbon dioxide for each ton of olefin product.

[0007] An alternative source of olefins is via the conversion of natural gas produced from shale deposits. Various technologies are being explored for converting one or more components of natural gas into economically desirable olefins. One such reaction is the oxidative dehydrogenation of hydrocarbons to produce chemicals with lower saturation and water, such as the conversion of ethane to ethylene while producing water. In one form of oxidative dehydrogenation, an oxygen transfer agent is used to provide a source of oxygen for the reaction. Summary of the invention

[0008] It has been observed that at elevated temperatures, the oxygen transfer agent may not have adequate fluidization within the reactor used for the reaction, resulting in reduced yields of the desired product. Therefore, there is a need for an improved process for producing olefins using oxidative dehydrogenation in which adequate fluidization is maintained in the reactor at elevated temperatures. According to one or more embodiments described herein, it has been discovered that including a fluidization enhancing additive with the oxygen transfer agent allows for adequate fluidization of the oxygen transfer agent in the reactor at reaction temperatures.

[0009] According to various aspects, a method for the oxidative dehydrogenation of hydrocarbons to produce olefins and water includes contacting the hydrocarbons with a particulate material in a fluidized bed. The particulate material may include at least one oxygen transfer agent; and at least one fluidization enhancing additive composed of an inorganic material. During at least a portion of the time that the hydrocarbons are in contact with the particulate material, the fluidized bed is at a temperature equal to or greater than the melting point of one or more materials of the oxygen transfer agent. In addition, during at least a portion of the time that the hydrocarbons are in contact with the particulate material, the surface of at least a portion of the at least one oxygen transfer agent includes a molten layer. The at least one fluidization enhancing additive does not undergo reduction in the fluidized bed during the period that the hydrocarbons are in contact with the particulate material at the temperature. The at least one fluidization enhancing additive is present in an amount to keep the particulate material sufficiently fluidized.

[0010] It should be understood that both the foregoing summary and the following detailed description present embodiments of the present technology and are intended to provide an overview or framework for understanding the nature and features of the technology as claimed. The accompanying drawings are included to provide additional understanding of the technology and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments and, together with the description, serve to explain the principles and operation of the technology. In addition, the drawings and description are meant to be illustrative only and are not intended to limit the scope of the claims in any way.

[0011] Additional features and advantages of the described embodiments will be set forth in the detailed description that follows. Additional features and advantages of the described embodiments will be apparent to those skilled in the art in part through this description, or will be recognized through practice of the described embodiments (including the detailed description that follows), as well as the accompanying drawings and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The following detailed description of certain embodiments of the present disclosure may be best understood when taken in conjunction with the following drawings, in which like reference numerals are used to indicate like structures and in which:

[0013] Figure 1 shows the reduction / oxidation of oxygen transfer agents according to embodiments described herein with simultaneous formation of useful products;

[0014] Figure 2 is a schematic diagram of the apparatus used for laboratory-scale fluidization experiments;

[0015] Figure 3 is a plot of pressure differential versus superficial gas velocity from Example 1;

[0016] Figure 4 is a plot of pressure differential versus bed temperature from Example 2; and

[0017] Figure 5is a plot of ethane conversion versus olefin selectivity from Example 4. DETAILED DESCRIPTION

[0018] According to one or more embodiments described herein, a method for oxidative dehydrogenation of hydrocarbons to produce olefins and water may include contacting the hydrocarbons with a particulate material comprising at least one oxygen transfer agent (hereinafter referred to as "OTA") and at least one fluidization enhancing additive composed of an inorganic material in a fluidized bed. The method will now be described in more detail.

[0019] In one or more embodiments, the at least one fluidization enhancing additive is present in an amount sufficient to maintain the fluidization of the particulate material. The fluidization in the reactor can exist in a continuous gas-solid fluid state. For example, when the fluid seeps out only through the void space between the fixed particles, the resulting fluid state is referred to as a "fixed bed". Fluidization can then be carried out through some or all of "expanded bed", "minimum fluidization", "smooth fluidization", "bubbling fluidization", "throttle fluidization", "turbulent fluidization", "dense phase fluidization", "spouted bed fluidization", "channel flow", "dilute phase fluidization", "fast fluidization" and "dilution transport fluidization". These different types of fluidization are in Jakobsen HA (2009) Fluidized Bed Reactors. See: Chemical Reactor Modeling. Springer, Berlin, Heidelberg https: / / doi.org / 10.1007 / 978-3-540-68622-4_10 for a more detailed description. As used herein, the term "fluidized bed" refers to a reactor that exhibits minimum fluidization. When the fluidization enhancing additive is not included, the reactor may be similar to a fixed bed reactor due to the agglomeration of OTA at the reaction temperature originally desired for the oxidative dehydrogenation. However, the addition of the fluidization enhancing additive can maintain the minimum fluidization in which the particulate material is suspended in the reactor. As used herein, the term "maintain" includes situations in which the fluidization remains the same when the fluidization enhancing additive is added, situations in which the fluidization increases when the fluidization enhancing additive is added, and situations in which the fluidization is slightly reduced but not less than the minimum fluidization. Therefore, the fluidization enhancing additive can prevent the reactor from behaving as a fixed bed reactor, which significantly interferes with the oxidative dehydrogenation reaction. In some embodiments, the reactor can exist in a fast flow state, in which the solid content is continuously and gradually reduced above the height of the reactor, and there is no obvious interface between the dense bed of particulate material in the reactor and the liquid.

[0020] As described herein, oxidative dehydrogenation (hereinafter referred to as "ODH") can be used to form olefins. In one or more embodiments, ODH of hydrocarbons (e.g., paraffins) provides an olefin production route that can significantly reduce CO2 emissions and virtually eliminate NOx emissions from world-scale plants relative to conventional olefin production routes. ODH is an exothermic, selective catalytic process that primarily produces olefins and water as products. Reaction scheme (1) provides a general ODH reaction:

[0021] ZGar n H 2n+2-2β +(z-1+δ)[O]→C zxn H 2(zxn)+2-2β-2δ +(z-1+δ)H2O (1)

[0022] Wherein z = the number of reacting chain alkane molecules; n = the number of atomic units in the reacting molecules; β = the degree of unsaturation, with a value of zero for single bonds, a value of one for double bonds and molecular rings, and a value of two for triple bonds; and δ = the change in the degree of unsaturation. The oxygen [O] in reaction scheme (1) can be provided by the reduction of a metal oxide or by the catalytic use of molecular oxygen. When n = 1, the reaction shown in reaction scheme (1) is referred to as the "oxidative coupling of methane". Reaction scheme (2) shows an exemplary oxidative dehydrogenation of ethane to ethylene, i.e., the reaction when n = 2. As described above, the reaction is exothermic, producing 105 kJ of heat per mole of ethane converted.

[0023] CH3CH3+1 / 2O2→CH2CH2+H2O ΔH°=-105kJ / mol (2)

[0024] The ODH reaction can be carried out in the presence of a particulate material comprising at least one OTA and at least one fluidization enhancing additive. In some embodiments, the at least one OTA and the at least one fluidization enhancing additive are separate particles in the particulate material. In some embodiments, the particulate material includes particles that combine the at least one oxygen transfer agent and the at least one fluidization enhancing additive. OTA and fluidization enhancing additives will now be described in more detail.

[0025] When any reaction according to reaction scheme (1) promotes the conversion of hydrocarbons, OTA is reduced from an oxidized state to a less oxidized reduced state. To regenerate OTA, oxygen can be used to reoxidize the reduced OTA. The reoxidation process can occur simultaneously with the reduction of the oxygen transfer agent in the presence of one or more oxidants such as oxygen, air, carbon dioxide, steam, NOx and / or sulfur oxides. Alternatively, OTA can be reoxidized in a separate step. Figure 1This reduction / oxidation of OTA, schematically shown in , and the simultaneous formation of useful products is generally described as a redox or chemical cyclization system. In embodiments, OTA may include compounds that undergo reduction during ODH, thereby providing oxygen for the formation of water.

[0026] In embodiments, the surface of at least a portion of the OTA comprises a molten layer during at least a portion of the time that the hydrocarbon is in contact with the particulate material. The molten layer may comprise from 1% to 100% of the surface area of ​​the outer surface of the OTA, such as from 1% to 95%, 1% to 90%, 1% to 85%, 1% to 80%, 1% to 75%, 1% to 70%, 1% to 65%, 1% to 60%, 1% to 55%, 1% to 50%, 1% to 45%, 1% to 40%, 1% to 35%, 1% to 30%, 1% to 25%, 1% to 20%, 1% to 100% of the surface area of ​​the outer surface of the OTA. % to 15%, 1% to 10%, 5% to 95%, 10% to 95%, 15% to 95%, 20% to 95%, 25% to 95%, 30% to 95%, 35% to 95%, 40% to 95%, 45% to 95%, 50% to 95%, 55% to 95%, 60% to 95%, 65% to 95%, 70% to 95%, 75% to 95%, 80% to 95%, or even 85% to 95%. Without being bound by theory, it is believed that molten layer formation occurs when OTA is exposed to a temperature close to or greater than the melting point of the OTA material. Such temperatures may exist in a fluidized bed reactor, such as at least 450°C.

[0027] In an embodiment, OTA may comprise an alkali metal and at least one of: a mixed oxide of at least one metal capable of oxidizing hydrocarbons to a more unsaturated state when in contact with hydrocarbons or coupling the formation of carbon-carbon bonds with water as in reaction scheme (1); and a mixed oxide of at least one metal capable of hydrogen oxidation when in contact with hydrogen. OTA may additionally comprise boron.

[0028] The mixed oxides included in the oxygen transfer agent can be prepared from materials from the cubic lattice family R6R'O8, where R and R' are different elements and O is oxygen. These materials are solid solutions of R' in R and have been observed to show very small changes in lattice parameters upon reduction or reoxidation, making them dimensionally stable as OTA. Examples of materials include Mg6MnO8, Cu6PbO8, and Ni6MnO8. In an embodiment, the at least one OTA may comprise a mixed oxide containing Mg6MnO8. In addition to a crystal structure that is stable upon redox cycling, these R6R'O8 materials can be prepared in a manner that produces a very dense, hard substrate. The addition of a small amount of boron can greatly increase the toughness of the particles.

[0029] In an embodiment, OTA may include at least one reducing metal-containing oxide; at least one alkali metal substance; at least one boron-containing substance; and at least one alkaline earth metal-containing substance. The at least one reducing metal-containing oxide may be selected from the group consisting of manganese oxide, tin oxide, indium oxide, germanium oxide, lead oxide, antimony oxide, bismuth oxide, praseodymium oxide, terbium oxide, cerium oxide, iron oxide, ruthenium oxide, and combinations of two or more thereof. The alkali metal substance may include elemental alkali metals or compounds containing alkali metals. The boron-containing substance may include elemental boron or compounds containing boron. The alkaline earth metal-containing substance may include elemental alkaline earth metals or compounds containing alkaline earth metals.

[0030] In an embodiment, the OTA may include a a B b C c O x A mixed oxide of wherein M is manganese, tin, indium, germanium, lead, antimony, bismuth, praseodymium, terbium, cerium, iron, ruthenium, or a combination of two or more thereof; L is at least one alkali metal; B is boron; C is at least one alkaline earth metal; O is oxygen; a is 0.01 to 10; b is 0.1 to 20; c is 0.1 to 100; and x is the number of oxygen atoms required due to the valence states of M, L, B and C.

[0031] In other embodiments, the OTA may include a b C c O x A mixed oxide of wherein M is manganese, tin, indium, germanium, lead, antimony, bismuth, praseodymium, terbium, cerium, iron, ruthenium, or a combination of two or more thereof; B is boron; C is at least one alkaline earth metal; O is oxygen; a is 0.01 to 10; b is 0.1 to 20; c is 0.1 to 100; and x is the number of oxygen atoms required due to the valence states of M, B and C.

[0032] In an embodiment, OTA may include a perovskite, which is a mineral having an ABX3 structure, wherein A and B are cations and X is an anion that forms a bond with the two cations, such as an oxide. Exemplary perovskites include CaMnO3, BaMnO 3-δ 、SrMnO 3-δ 、Mn2SiO4、Mn2MgO 4-δ ,La 0.8 Sr 0.2 ,La 0.8 FeO 3-δ 、Ca9Ti 0.1 Mn 0.9 O 3-δ 、Pr6O 11-δ , or a combination of two or more thereof.

[0033] In embodiments, OTA may further comprise one or more promoters that promote higher selectivity for a particular desired product. Although not wishing to be bound by any particular theory, it is believed that active oxygen is attracted to promoter sites within OTA, enabling OTA to act as a selective promoter for reaction scheme (1) and as an oxygen reservoir for a selective promoter. Exemplary promoters may include, for example, single metal and mixed metal oxides of Fe, Co, La, Sr, Sm, Pr, Y, Ga, Ce, Zr, Ti, W, Mo, V, Nb, and Cr, and dopants such as Ni, Sn, Ga, W, Zr, Na, K, Cs, Rb, As, Sb, Bi, and P. Other promoters may include silicates or aluminates of alkali or alkaline earth metals, such as silicates and aluminates of sodium, lithium, calcium, and barium. In addition, silicates and aluminates of manganese (bronzeite), iron, zirconium, copper, or ruthenium may be used. Another class of oxygen flux promoters that may be used includes oxides having a pore structure that promotes oxygen anion transport, such as cerium oxide, zinc oxide, zirconium oxide (with or without additives such as yttrium), praseodymium oxide, or barium oxide. In embodiments, the promoter includes tungsten and an alkali metal, an alkaline earth metal, or a combination of an alkali metal and an alkaline earth metal.

[0034] In embodiments, the particle size of OTA may be 10 μm to 200 μm, 10 μm to 190 μm, 10 μm to 180 μm, 10 μm to 170 μm, 10 μm to 160 μm, 10 μm to 150 μm, 10 μm to 140 μm, 10 μm to 130 μm, 10 μm to 120 μm, 10 μm to 110 μm, 10 μm to 100 μm, 10 μm to 90 μm, 10 μm to 80 μm, 10 μm to 70 μm, 10 μm to 60 μm, 10 μm to 50 μm, 10 μm to 40 μm, 10 μm to 30 μm, 10 μm to 20 In some embodiments, the present invention relates to a thickness of at least 1 μm, 20 μm to 200 μm, 30 μm to 200 μm, 40 μm to 200 μm, 50 μm to 200 μm, 60 μm to 200 μm, 70 μm to 200 μm, 80 μm to 200 μm, 90 μm to 200 μm, 100 μm to 200 μm, 110 μm to 200 μm, 120 μm to 200 μm, 130 μm to 200 μm, 140 μm to 200 μm, 150 μm to 200 μm, 160 μm to 200 μm, 170 μm to 200 μm, 180 μm to 200 μm, or even 190 μm to 200 μm. Particle size distribution can be measured in aqueous dispersion using ASTM method D4464-15, the entire contents of which are incorporated herein by reference, wherein the particle refractive index is 1.730. Instruments used to perform the measurement may include, for example, a Mastersizer 2000.

[0035] In one or more embodiments, OTA may exhibit characteristics known in the industry as "Geldart A" characteristics. In other embodiments, OTA may exhibit characteristics known in the industry as "Geldart B" characteristics. According to D. Geldart, Gas Fluidization Technology, John Wiley & Sons (New York, 1986), 34-37 and D. Geldart, "Types of Gas Fluidization," Powder Technol. 7 (1973) 285-292 (the entire contents of which are incorporated herein by reference), particle types can be classified as "Group A" or "Group B".

[0036] As used herein, the term "Group A" refers to aerated powders having the following properties: a bubble-free range of fluidization; high bed expansion; slow and linear degassing rates; bubble characteristics, which may include a predominance of split / recoalescing bubbles, with maximum bubble size and large wakes; high levels of solid mixing and gas backmixing, assuming equal U-umf (U is the velocity of the carrier gas, and Umf is the minimum fluidizing velocity, usually but not necessarily measured in meters per second (m / s), i.e., excessive gas velocities exist); axisymmetric bulk characteristics; and no spurting except in very shallow beds. Assuming equal particle size As the average particle size decreases; or as The listed properties tend to improve as the proportion of particles smaller than 45 μm increases; or as the pressure, temperature, viscosity and density of the gas increase. In general, the particles may exhibit a small average particle size and / or a low particle density (ρρ) (<1.4 g / cm3, g / cm 3 ); easy fluidization, with smooth fluidization at low gas velocities; and can exhibit controlled bubbling with small bubbles at higher gas velocities.

[0037] As used herein, the term "Group B" refers to "sand-like" powders that: begin bubbling at Umf; exhibit moderate bed expansion; exhibit rapid degassing; have no restrictions on bubble size; have moderate levels of solid mixing and gas backmixing, assuming equal U-umf; include both axisymmetric and asymmetric lumps; and exhibit spurting only in shallow beds. These properties tend to improve as the average particle size decreases, but particle size distribution and some uncertainty in gas, pressure, temperature, viscosity, or density appear to play little role in improving the properties. In general, when the majority of Group B particles have Granularity When the density (ρρ) is 1.4 <pp<4g / cm 3 .when for When ρρ is 4g / cm3 , and when for When the density (ρρ) is about 1g / cm 3 .

[0038] The fluidization of Geldart A and Geldart B sized particles such as OTA described herein can be improved by introducing fine particles having a size of 10 μm to 200 μm. According to the embodiments described herein, inter-particle agglomeration caused by surface adhesion between particles is controlled by introducing a fluidization enhancing additive. In this way, OTA, which is not practical for oxidative dehydrogenation without a fluidization enhancing additive, can be practically used in fluidized bed and moving bed reactors. Similarly, a fluidization enhancing additive can allow particle size adjustment. Therefore, if the manufacturing method for producing OTA cannot effectively produce a desired range of particle sizes, a fluidization enhancing additive can be added to the formed OTA during manufacturing.

[0039] Fluidization enhancing additives will now be described in more detail. The at least one fluidization enhancing additive may not undergo reduction in the fluidized bed during contact of the hydrocarbon with the particulate material. Exemplary fluidization enhancing additives include non-reducing oxides, zeolites, clays, fluidized catalytic cracking catalysts, and combinations of two or more thereof. Other exemplary fluidization enhancing additives include non-reducing oxides containing inorganic materials, which include chemicals selected from aluminum oxide, silicon dioxide, silicon carbide, metal carbides, metal nitrides, titanium dioxide, alkaline earth metal oxides, alkali metal sulfates, alkaline earth metal sulfates, calcium sulfate, calcium sulfate hydrates, alkali metal carbonates, alkaline earth metal carbonates, lanthanum oxide, rare earth metal oxides, boric acid, borates, boron oxide, zinc oxide, cerium oxide, gallium oxide, and combinations of two or more thereof.

[0040] In embodiments, the fluidization enhancing additive may comprise a zeolite such as Formula M 2 / n O·Al2O3ySiO2wH2O zeolite, wherein y is an integer from 2 to 1,000,000,000; n is the valence of the cationic portion of the at least one zeolite; M is a metal selected from Zr, Mg, Ti, and a combination of two or more thereof; and w is the number of water molecules per zeolite unit structure, such that at least 5% of n is attributed to proton charge. For example, the zeolite may include zeolite Y, zeolite A, faujasite, bentonite, sodalite, ZSM-10, MCM-68, MCM-61, MCM-35, ZSM-39, ZSM-23, ZSM-12, SAPO 56, AlPO-5, AlPO-14, AlPO-41, or a combination of two or more thereof.

[0041] In an embodiment, the fluidization enhancement additive may include a fluidized catalytic cracking (hereinafter referred to as "FCC") catalyst. As described herein, FCC catalysts are those materials generally known to have a cracking catalytic function. However, it should be understood that such FCC catalysts described herein may not operate with the cracking function in the system and method of the present disclosure (i.e., they may be sufficiently inert). FCC catalysts may include crystalline zeolites, matrices, binders, and fillers. Typically, zeolites, such as Y-type zeolites, are active materials and may account for about 15% to 50% by weight of the catalyst. An exemplary matrix is ​​alumina, which may also contribute catalytic active sites. Binder and filler components, such as silica sol and kaolin, may provide physical strength to the catalyst, respectively. In order to be used as a fluidization enhancement additive, the fluidized catalytic cracking catalyst may be fresh, balanced, and / or stabilized. As used herein, the term "fresh catalyst" refers to a catalyst that has not yet been used in an FCC process. As used herein, the term "balanced catalyst" refers to a catalyst that has been used in an FCC process and has lost more than 50% of its activity relative to its activity as a fresh catalyst. As used herein, the term "stabilized catalyst" refers to an FCC catalyst that contains additives or whose zeolite has been modified to promote stability such that the activity of the FCC catalyst is greater than the activity of an otherwise identical unstabilized FCC catalyst.

[0042] In embodiments, the particle size of the fluidization enhancing additive may be from 10 μm to 200 μm, from 10 μm to 190 μm, from 10 μm to 180 μm, from 10 μm to 170 μm, from 10 μm to 160 μm, from 10 μm to 150 μm, from 10 μm to 140 μm, from 10 μm to 130 μm, from 10 μm to 120 μm, from 10 μm to 110 μm, from 10 μm to 100 μm, from 10 μm to 90 μm, from 10 μm to 80 μm, from 10 μm to 70 μm, from 10 μm to 60 μm, from 10 μm to 50 μm, from 10 μm to 40 μm, from 10 μm to 30 μm, from 10 μm to 40 μm. 20μm, 20μm to 200μm, 30μm to 200μm, 40μm to 200μm, 50μm to 200μm, 60μm to 200μm, 70μm to 200μm, 80μm to 200μm, 90μm to 200μm, 100μm to 200μm, 110μm to 200μm, 120μm to 200μm, 130μm to 200μm, 140μm to 200μm, 150μm to 200μm, 160μm to 200μm, 170μm to 200μm, 180μm to 200μm, or even 190μm to 200μm.

[0043] The OTA and fluidization enhancing additives described herein can be used in a process for the oxidative dehydrogenation of hydrocarbons. In an embodiment, a particulate material comprising both OTA and a fluidization enhancing additive can be added to a fluidized bed reactor, wherein the hydrocarbons can contact the particulate material. In other embodiments, the particulate material can comprise OTA, but the fluidization enhancing additive can be added to the fluidized bed reactor alone. As described above, the fluidization enhancing additive can maintain fluidization within the reactor so that the reactor does not behave as a fixed bed reactor.

[0044] In embodiments, the weight ratio of OTA to fluidization enhancing additive may be from 50:50 to 99:1, 50:50 to 95:5, 50:50 to 90:10, 50:50 to 85:15, 50:50 to 80:20, 50:50 to 75:25, 50:50 to 70:30, 50:50 to 65:35, 50:50 to 60:40, 55:45 to 99:1:10, 60:40 to 99:1, 65:35 to 99:1, 70:30 to 99:1, 75:25 to 99:1, 80:20 to 99:1, 85:15 to 99:1, 90:10 to 99:1, or even 95:5 to 99:1. Without wishing to be bound by any particular theory, it is believed that when the concentration of the fluidization enhancing additive is too high, OTA may not be able to perform its function in the oxidative dehydrogenation or at least may be largely hindered. However, when the concentration of the fluidization enhancing additive is too low, fluidization is impaired for the reasons fully described above.

[0045] During at least a portion of the time that the hydrocarbon is in contact with the particulate material, the fluidized bed is at a temperature equal to or greater than the melting point of one or more materials of the OTA. As used herein, the term "temperature" refers to the average temperature within the fluidized bed reactor when the hydrocarbon is in contact with the OTA and the fluidization enhancing additive. In embodiments, the temperature is at least 350°C. In embodiments, the temperature is at least 450°C. In embodiments, the temperature is at least 650°C. For example, the temperature may be 650°C to 1500°C, 650°C to 1450°C, 650°C to 1400°C, 650°C to 1350°C, 650°C to 1300°C, 650°C to 1250°C, 650°C to 1200°C, 650°C to 1150°C, 650°C to 1100°C, 650°C to 1050°C, 650°C to 1000°C, 650°C to 950°C, 650°C to 900°C, 650°C to 850°C, 650°C to 800°C, 650°C to 750°C. , 700°C to 1500°C, 750°C to 1500°C, 800°C to 1500°C, 850°C to 1500°C, 900°C to 1500°C, 950°C to 1500°C, 1000°C to 1500°C, 1050°C to 1500°C, 1100°C to 1500°C, 1150°C to 1500°C, 1200°C to 1500°C, 1250°C to 1500°C, 1300°C to 1500°C, 1350°C to 1500°C, or even 1400°C to 1500°C. The surface of at least a portion of the at least one OTA may include a molten layer for contacting at least a portion. Without wishing to be bound by any particular theory, it is believed that higher temperatures increase the reaction rate, but higher temperatures may also result in changes in product selectivity. For example, higher temperatures may result in the formation of more aromatic compounds and butadiene, coke, and COx.

[0046] Other parameters within the fluidized bed reactor include the gas hourly space velocity (GHSV), the superficial gas velocity, and the amount of carrier gas required to maintain the OTA and fluidization enhancing additive in a fluidized state. It has been found that the GHSV of the process of the present invention is from about 100 to about 150,000 standard cubic meters per hour of hydrocarbon feed per cubic meter of bulk density of OTA and fluidization enhancing additive (h -1 ), such as 1,000h -1 Up to 10,000h -1 or 1,000h -1 Up to 5,000h -1. OTA and fluidization enhancing additives can be pneumatically moved through the reaction system by a carrier fluid such as an inert diluent fluid or one of the reactants in gaseous form. Examples of inert diluent carrier gases (sometimes also referred to as "superficial gases") are nitrogen, volatile hydrocarbons (e.g., methane), steam, carbon dioxide, argon, and other carriers that do not interfere with the reaction. This list should not be considered exhaustive. The carrier fluid (or superficial gas) velocity in the reactor during the reaction may be 0.1 m / s to 25 m / s, such as 0.5 m / s to 20 m / s, 1 m / s to 15 m / s, or 5 m / s to 15 m / s, depending on the surface area of ​​the reactor. The amount of carrier gas required is only the amount necessary to keep OTA and fluidization enhancing additives in a fluidized state. Preferably, the amount of carrier gas used may be in the range of about 0 kg gas to about 0.2 kg gas per kg OTA and fluidization enhancing additive. Alternatively, OTA and fluidization enhancing additives may be transported through the reactor at a pressure below atmospheric pressure without a diluent.

[0047] According to one aspect, alone or in combination with any other aspect, a method for oxidative dehydrogenation of hydrocarbons to produce olefins and water comprises: contacting hydrocarbons with a particulate material in a fluidized bed. The particulate material may include at least one oxygen transfer agent; and at least one fluidization enhancing additive composed of an inorganic material. During at least a portion of the time that the hydrocarbon is in contact with the particulate material, the fluidized bed is at a temperature equal to or greater than the melting point of one or more materials of the oxygen transfer agent. In addition, during at least a portion of the time that the hydrocarbon is in contact with the particulate material, the surface of at least a portion of the at least one oxygen transfer agent includes a molten layer. The at least one fluidization enhancing additive does not undergo reduction in the fluidized bed during the period that the hydrocarbon is in contact with the particulate material at the temperature. The at least one fluidization enhancing additive is present in an amount to keep the particulate material sufficiently fluidized.

[0048] According to a second aspect, alone or in combination with any other aspect, the at least one oxygen transfer agent and the at least one fluidization enhancing additive are separate particles in the particulate material.

[0049] According to a third aspect, alone or in combination with any other aspect, the particulate material comprises particles comprising the at least one oxygen transfer agent and the at least one fluidization enhancing additive.

[0050] According to a fourth aspect, alone or in combination with any other aspect, the at least one oxygen transfer agent comprises a compound that undergoes reduction during the oxidative dehydrogenation thereby providing oxygen for forming water.

[0051] According to a fifth aspect, alone or in combination with any other aspect, the at least one oxygen transfer agent comprises a mixed oxide comprising Mg6MnO8.

[0052] According to a sixth aspect, alone or in combination with any other aspect, the at least one oxygen transfer agent further comprises at least two promoters, the at least two promoters comprising tungsten and an alkali metal, an alkaline earth metal, or a combination of an alkali metal and an alkaline earth metal.

[0053] According to the seventh aspect, alone or in combination with any other aspect, the at least one oxygen transfer agent comprises: at least one reducing metal oxide selected from the group consisting of: manganese oxide, tin oxide, indium oxide, germanium oxide, lead oxide, antimony oxide, bismuth oxide, praseodymium oxide, terbium oxide, cerium oxide, iron oxide, ruthenium oxide and combinations of two or more thereof; at least one alkali metal substance, the alkali metal substance comprising elemental alkali metal or a compound containing alkali metal; at least one boron-containing substance, the boron-containing substance comprising elemental boron or a compound containing boron; and at least one alkaline earth metal-containing substance, the alkaline earth metal-containing substance comprising elemental alkaline earth metal or a compound containing alkaline earth metal.

[0054] According to the eighth aspect, alone or in combination with any other aspect, the at least one oxygen transfer agent comprises formula ML a B b C c O x A mixed oxide of wherein M is selected from the group consisting of manganese, tin, indium, germanium, lead, antimony, bismuth, praseodymium, terbium, cerium, iron, ruthenium and combinations of two or more thereof; L is at least one alkali metal; B is boron; C is at least one alkaline earth metal; O is oxygen; a is 0.01 to 10; b is 0.1 to 20; c is 0.1 to 100; and x is the number of oxygen atoms required due to the valence states of M, L, B and C.

[0055] According to the ninth aspect, alone or in combination with any other aspect, the at least one oxygen transfer agent comprises formula MB b C c O x A mixed oxide of wherein M is selected from the group consisting of manganese, tin, indium, germanium, lead, antimony, bismuth, praseodymium, terbium, cerium, iron, ruthenium and combinations of two or more thereof; B is boron; C is at least one alkaline earth metal; O is oxygen; a is 0.01 to 10; b is 0.1 to 20; c is 0.1 to 100; and x is the number of oxygen atoms required due to the valence states of M, L, B and C.

[0056] According to a tenth aspect, alone or in combination with any other aspect, the oxygen transfer agent is a perovskite.

[0057] According to the eleventh aspect, alone or in combination with any other aspect, the oxygen transfer agent comprises CaMnC3, BaMnO 3-δ 、SrMnC 3-δ、Mn2SiO4、Mn2MgO 4-δ ,La 0.8 Sr 0.2 ,La 0.8 FeO 3-δ 、Ca9Ti 0.1 Mn 0.9 O 3-δ 、Pr6O 11-δ , or a combination of two or more thereof.

[0058] According to a twelfth aspect, alone or in combination with any other aspect, the fluidised bed is at a temperature of at least 650°C during at least a portion of the time that the hydrocarbons are in contact with the particulate material.

[0059] According to a thirteenth aspect, alone or in combination with any other aspect, the fluidised bed is at a temperature of 650°C to 1500°C during at least a portion of the time that the hydrocarbons are in contact with the particulate material.

[0060] According to a fourteenth aspect, alone or in combination with any other aspect, the fluidization enhancing additive is selected from the group consisting of non-reducing oxides, zeolites, clays, fluid catalytic cracking catalysts, and combinations of two or more thereof.

[0061] According to the fifteenth aspect, alone or in combination with any other aspect, the fluidization enhancing additive comprises a non-reducing oxide containing an inorganic material, the inorganic material including a chemical selected from the group consisting of: aluminum oxide, silicon dioxide, silicon carbide, metal carbides, metal nitrides, titanium dioxide, alkaline earth metal oxides, alkali metal sulfates, alkaline earth metal sulfates, calcium sulfate, calcium sulfate hydrate, alkali metal carbonates, alkaline earth metal carbonates, lanthanum oxide, rare earth metal oxides, boric acid, borates, boron oxide, zinc oxide, cerium oxide, gallium oxide, and combinations of two or more thereof.

[0062] According to the sixteenth aspect, alone or in combination with any other aspect, the fluidization enhancing additive comprises at least one of formula M 2 / n O Al2O3ySiO2wH2O zeolite, wherein y is an integer from 2 to 1,000,000,000; n is the valence of the cationic portion of the at least one zeolite; M is a metal selected from Zr, Mg, Ti and a combination of two or more thereof; and w is the number of water molecules per zeolite unit structure, such that at least 5% of n is attributed to proton charge.

[0063] According to the seventeenth aspect, alone or in combination with any other aspect, the at least one zeolite of formula (3) is selected from the group consisting of: zeolite Y, zeolite A, faujasite, bentonite, sodalite, ZSM-10, MCM-68, MCM-61, MCM-35, ZSM-39, ZSM-23, ZSM-12, SAPO 56, AlPO-5, AlPO-14, AlPO-41 and a combination of two or more thereof.

[0064] According to an eighteenth aspect, alone or in combination with any other aspect, the fluidization enhancing additive comprises at least one fluid catalytic cracking catalyst.

[0065] According to a nineteenth aspect, alone or in combination with any other aspect, the at least one fluid catalytic cracking catalyst is fresh.

[0066] According to a twentieth aspect, alone or in combination with any other aspect, the at least one fluid catalytic cracking catalyst is balanced.

[0067] According to a twenty-first aspect, alone or in combination with any other aspect, the at least one fluid catalytic cracking catalyst is stabilized by adding one or more additives.

[0068] In accordance with a twenty-second aspect, alone or in combination with any other aspect, the one or more additives include lanthanum.

[0069] According to a twenty-third aspect, alone or in combination with any other aspect, the weight ratio of the at least one oxygen transfer agent to the at least one fluidization enhancing additive is from 50:50 to 99:1.

[0070] One or more features of the present disclosure are described in view of the following embodiments:

[0071] Example

[0072] The following examples are illustrative in nature and should not be used to limit the scope of the present application.

[0073] Preliminary considerations

[0074] For the following experiments, the fluidization enhancing additive comprises the formula M 2 / nO·Al2O3·ySiO2·wH2O zeolite, wherein y is an integer from 2 to 1,000,000,000; n is the valence of the cationic portion of the at least one zeolite; M is a metal selected from Zr, Mg, Ti and a combination of two or more thereof; and w is the number of water molecules per zeolite unit structure, such that at least 5% of n is attributed to proton charge. An exemplary OTA referred to as "OTA3" in the following examples is sodium tungstate on the surface of Mg6MnO. The OTA can be prepared as follows: MgO (1,692 g), MnO2 (1,288 g), H3BO3 (452 ​​g), Na4P2O7 (1,481 g), ammonium metatungstate (258 g) and 30% colloidal silica sol (858 g) are dry mixed. 5 l of distilled water is added to the dry mixture. The mixture is spray dried to produce an average particle size of 70 μm. The resulting particles were calcined in air at 950°C for 12 hours to produce the final OTA.

[0075] OTA and the fluidization enhancing additive are premixed in a weight ratio of OTA to fluidization enhancing additive of 50:50 to 90:10.

[0076] Laboratory-scale fluidization experiments are conducted in Figure 2 The reactor 10 is carried out in a quartz bubble bed flow reactor having an inner diameter of 2.54 cm (1 inch) as shown. The reactor 10 is capable of reaching temperatures up to 1100° C. The reactor is equipped with two dielectric glass frits 14 on the inlet side 16 for loading the catalyst mixture 18 thereon. There are four ports on the outlet side 20 for a 12-point thermocouple 22, a gas outlet 24, and a high branch 26 and a low branch 28 of a differential pressure (DP) device 30. A nitrogen backflush 32 operated at 10 sccm on the high branch 26 of the DP prevents fine particles from contaminating the DP. Gas is supplied to the reactor through the inlet 34 by a mass flow controller, and the Camile data acquisition and control system is used to control the device operation.

[0077] In a typical room temperature fluidization experiment, the thermocouple and DP tube are first installed, and then the OTA / fluidization enhancement additive mixture or pure material is loaded. The pure material is premixed and then poured into the reactor. The reactor is then checked for leaks and the N2 flow is started. The DP is measured every 30 seconds, and the DP readings are collected for three minutes at each N2 flow rate. The N2 flow rate is typically in the range of between 75sccm and 4000sccm. These experiments reveal the fluidizability of the material (from the DP readings), and also measure the minimum fluidization velocity (U) of the fluidizable material. mf ).

[0078] For high temperature experiments, at various temperatures, the mfDP is measured at a constant superficial gas (N2) velocity of 100 ℃. Therefore, as the temperature increases, the volumetric flow rate of N2 is reduced to maintain a constant superficial velocity. The temperature of the pure material or mixture is increased from room temperature to 300℃ at 5℃ / min under N2. DP is measured at temperatures between 300℃ and 1000℃. DP readings are collected at 30 second intervals for 1 hour at each temperature.

[0079] Example 1: Improving fluidization

[0080] 60 g of OTA (OTA1) showing poor fluidization distribution was charged into the reactor and the N2 velocity was increased to 0.14 m / s. Figure 3 As shown in Figure 1, which is a graph of DP versus N2 velocity, very low DP readings were recorded at all N2 flow rates, and the DP values ​​did not change significantly with flow rate. This behavior is consistent with a material having poor fluidization properties.

[0081] Next, a mixture of 10 g OTA1 and 10 g FCC catalyst (as a fluidization enhancing additive) was charged into the reactor, and the N2 velocity was increased to 0.12 m / s. Figure 3 As shown, significantly higher DP readings are observed, even at lower material loadings. The variation of DP with gas velocity exhibits the following pattern. At low flow rates, the system behaves like a fixed bed, where DP increases linearly with gas velocity until a maximum DP is reached. The gas velocity at maximum DP is the minimum fluidization velocity (U) at which the pressure drop equals the bed weight. mf ). Further increase of gas velocity (>U mf ) leads to fluidization of the bed, and the DP value remains almost constant at all subsequent gas velocities, such as Figure 3 The bed fluidization / bubbling of the mixture of OTA1 and fluidization enhancing additive also occurs when the gas velocity > U mf Confirm by visual inspection.

[0082] As a control experiment, 20 g of pure FCC catalyst fluidization enhancement additive was loaded into the reactor and the N2 velocity was increased to 0.12 m / s. The DP readings of the FCC catalyst alone were similar to those of the OTA1 + FCC catalyst system, such as Figure 3 Thus, the addition of FCC catalyst to OTA1 significantly improved the room temperature fluidization of OTA1, and the OTA1+FCC mixture behaved similarly to pure FCC catalyst from a fluidization point of view.

[0083] Example 2: Increasing the reaction temperature

[0084] 20 g of OTA (i.e., OTA2) showing good fluidization characteristics at room temperature was charged into the reactor. OTA2 (20 g) was fluidized at temperatures between 300°C and 800°C, and then DP was measured at each temperature at a constant superficial gas (N2) velocity. DP did not change at 300°C and 400°C, and was significantly lower at temperatures equal to and above 500°C, as shown in Figure 2. Figure 4 , which is a graph of DP versus bed temperature. The decrease in DP at and above 500°C is consistent with defluidization of OTA2, which results in channeling of the gas. Therefore, 500°C is expected to be the temperature limit for the oxidative dehydrogenation of hydrocarbons using OTA2. However, in order for this process to be economically viable for the oxidative dehydrogenation of ethane, 500°C is insufficient and a higher operating temperature is required. When 4 g of FCC catalyst fluidization enhancing additive was mixed with 16 g of OTA2, providing a weight ratio of OTA to fluidization enhancing additive of 80:20, the DP did not change significantly between 300°C and 750°C, and then decreased significantly at 800°C, as shown in FIG. Figure 4 As shown in , it is a graph of DP versus bed temperature. Figure 4 As shown, pure FCC catalyst fluidization enhancing additive (40 g) did not show any signs of defluidization at temperatures up to 900° C. Thus, adding a small amount of FCC catalyst fluidization enhancing additive to OTA2 resulted in an increase in operating temperature (“ΔT”) of approximately 300° C.

[0085] Example 3: Maintenance of reaction yield

[0086] A 5 ml sample of OTA3 prepared as described above was added to an alumina reactor with an inner diameter of 19 mm (0.75 in). Ethane was heated at 840 °C and 4,000 h. -1 Up to 4,800h -1 The conversion was carried out on OTA3 at a GHSV of 1.3 % and the conversion results are shown in Table 1. The catalyst bed was reverse fluidized at about 810°C.

[0087]

[0088] Next, a 5 ml sample of OTA3 was charged to the same alumina reactor also containing 5 ml of the equilibrium FCC catalyst fluidization enhancing additive. An ethane conversion run was conducted at 840°C, with the conversion results shown in Table 2. The GHSV was calculated based on the amount of OTA3. There was no evidence of any catalyst backfluidization at 840°C. Thus, these two experiments show that the addition of the FCC catalyst fluidization enhancing additive greatly improves the fluidization of the reactor components at the desired conversion temperature of 840°C, and the addition of the additive does not adversely affect the overall yield of the desired olefin products.

[0089]

[0090]

[0091] Example 4: Pilot scale oxidative dehydrogenation

[0092] Figure 5 1 is a graph of ethane conversion versus olefin selectivity showing the results of ethane oxydehydrogenation runs in a continuous circulating fluidized bed pilot unit reactor using 5 kg to 8 kg of total OTA and FCC catalyst fluidization enhancing additive. OTA similar to OTA3 was mixed with FCC catalyst fluidization enhancing additive in a mixture with a weight ratio of OTA to FCC catalyst fluidization enhancing additive ranging from 100:0 to 50:50. Figure 5 The results obtained from the pilot scale experiments shown in show that the pilot scale reactor provides similar conversion and selectivity as the results of the bench scale experiments provided in Tables 1 and 2. In addition, including 10% to 50% of the FCC catalyst fluidization enhancing additive in the pilot scale reactor allows reaction temperatures as high as 825°C.

[0093] It should be apparent to those skilled in the art that various modifications may be made to the described embodiments without departing from the essence and scope of the claimed subject matter. Therefore, this specification is intended to cover modifications and variations of the described embodiments as long as these modifications and variations fall within the scope of the appended claims and their equivalents.

Claims

1. A process for the oxidative dehydrogenation of hydrocarbons to produce olefins and water, the process comprising: The hydrocarbon is contacted in a fluidized bed with a particulate material consisting of: An oxygen transfer agent, wherein the oxygen transfer agent comprises an alkali metal and at least one of the following: a mixed oxide of at least one metal, the mixed oxide of at least one metal being capable of oxidizing the hydrocarbon to a more unsaturated state or as in reaction scheme (1) zC when contacted with the hydrocarbon n H 2n+2-2β +(z-1+δ)[O]→C z×n H 2(z×n)+2-2β-2δ +(z-1+δ)H2O, where z=the number of reacting paraffin molecules, n=the number of atomic units in the reacting molecules, β=the degree of unsaturation, with a value of zero for single bonds, a value of one for double bonds and molecular rings, a value of two for triple bonds, and δ=the change in the degree of unsaturation; and a mixed oxide of at least one metal capable of hydrogen oxidation when in contact with hydrogen; and at least one fluidization enhancing additive comprised of an inorganic material; in: During at least a portion of the time that the hydrocarbon is in contact with the particulate material, the fluidized bed is at a temperature at or above the melting point of the one or more materials of the oxygen transfer agent; During at least a portion of the time that the hydrocarbon is in contact with the particulate material, a surface of at least a portion of the oxygen transfer agent is exposed to a temperature near or greater than a melting point of the oxygen transfer agent material such that at least a portion of the oxygen transfer agent is a molten layer; said at least one fluidization enhancing additive comprised of an inorganic material does not undergo reduction in said fluidized bed during contacting of said hydrocarbon with said particulate material at said temperature; and The at least one fluidization enhancing additive comprised of an inorganic material is present in an amount to maintain sufficient fluidization of the particulate material.

2. The method of claim 1, wherein the oxygen transfer agent comprises a compound that undergoes reduction during the oxidative dehydrogenation thereby providing oxygen for forming water.

3. The method according to claim 1 or claim 2, wherein the oxygen transfer agent comprises: A mixed oxide comprising Mg6MnO8.

4. The method of claim 3, wherein the oxygen transfer agent further comprises at least two promoters, the promoters comprising tungsten and an alkali metal, an alkaline earth metal, or a combination of an alkali metal and an alkaline earth metal.

5. The method of claim 1 or claim 2, wherein the oxygen transfer agent comprises: at least one reducing metal-containing oxide selected from the group consisting of manganese oxide, tin oxide, indium oxide, germanium oxide, lead oxide, antimony oxide, bismuth oxide, praseodymium oxide, terbium oxide, cerium oxide, iron oxide, ruthenium oxide, and combinations of two or more thereof; at least one alkali metal species, the alkali metal species comprising an elemental alkali metal or a compound comprising the alkali metal; at least one boron-containing substance comprising elemental boron or a compound comprising boron; and At least one alkaline earth metal-containing substance, the alkaline earth metal-containing substance comprising elemental alkaline earth metal or a compound comprising an alkaline earth metal.

6. The method of claim 5, wherein the oxygen transfer agent comprises a mixed oxide of formula (1): ML a B b C c O x (1) in M is selected from the group consisting of manganese, tin, indium, germanium, lead, antimony, bismuth, praseodymium, terbium, cerium, iron, ruthenium, and combinations of two or more thereof; L is at least one alkali metal; B is boron; C is at least one alkaline earth metal; O is oxygen; a is 0.01 to 10; b is 0.1 to 20; c is from 0.1 to 100; and x is the number of oxygen atoms required due to the valence states of M, L, B and C.

7. The method of claim 5, wherein the oxygen transfer agent comprises a mixed oxide of formula (2): MB b C c O x (2) in M is selected from the group consisting of manganese, tin, indium, germanium, lead, antimony, bismuth, praseodymium, terbium, cerium, iron, ruthenium, and combinations of two or more thereof; B is boron; C is at least one alkaline earth metal; O is oxygen; a is 0.01 to 10; b is 0.1 to 20; c is from 0.1 to 100; and x is the number of oxygen atoms required due to the valence states of M, L, B and C.

8. The method of claim 1 or claim 2, wherein the oxygen transfer agent comprises a perovskite.

9. A process according to claim 1 or claim 2 wherein the fluidised bed is at a temperature of from 650°C to 1500°C during at least a portion of the time that the hydrocarbon is in contact with the particulate material.

10. The method of claim 1 or claim 2, wherein the fluidization enhancing additive is selected from the group consisting of: a non-reducing oxide containing an inorganic material, the inorganic material comprising a chemical selected from the group consisting of: alumina, silica, silicon carbide, metal carbides, metal nitrides, titanium dioxide, alkaline earth metal oxides, alkali metal sulfates, alkaline earth metal sulfates, calcium sulfate, calcium sulfate hydrate, alkali metal carbonates, alkaline earth metal carbonates, rare earth metal oxides, boric acid, borates, boron oxide, zinc oxide, gallium oxide, and combinations of two or more thereof; zeolites; clays; fluidized catalytic cracking catalysts, and combinations of two or more thereof.

11. The method according to claim 10, wherein the rare earth metal oxide is selected from lanthanum oxide and cerium oxide.

12. The method of claim 1 or claim 2, wherein the fluidization enhancing additive comprises at least one zeolite of formula (3): M 2 / n O·Al2O3·ySiO2·wH2O(3) in y is an integer from 2 to 1,000,000,000; n is the valence of the cationic portion of the at least one zeolite of formula (3); M is a metal selected from Zr, Mg, Ti and a combination of two or more thereof; and w is the number of water molecules per zeolite unit structure such that at least 5% of n is attributable to proton charges.

13. The process of claim 1 or claim 2, wherein the fluidization enhancing additive comprises at least one fluid catalytic cracking catalyst.

14. The process of claim 13, wherein the at least one fluid catalytic cracking catalyst is stabilized by the addition of one or more additives.

15. The method of claim 1 or claim 2, wherein the weight ratio of the oxygen transfer agent to the at least one fluidization enhancing additive is from 50:50 to 99:1.

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